David Raffaelli

Effects of the mussel Mytilus edulis L. on the invertebrate fauna of sediments

Two field experiments were carried out to investigate the effects of mussels (Mytilus edulis) on fauna and on sediment characteristics. In the first experiment mussels were removed from within an established mussel bed to create bare patches and in the second experiment mussels were transplanted to an adjacent bare sandflat. In the mussel removal experiment, mobile epibenthic crustaceans (predominately Gammarus spp. and Jaera albifrons) were markedly reduced in bare patches whereas infaunal species were much less affected. In the mussel transplant experiment, mobile epibenthic crustaceans (e.g. Gammarus spp. and Jaera albifrons) colonised mussel transplant plots, but were absent at all times from the adjacent sandflat sediments. The polychaetes Eteone longa and Pygospio elegans were both significantly reduced in mussel transplant plots, whilst Capitella spp. increased in numbers. Mussels clearly had marked effects on both the fauna and sediments probably through a combination of biodeposition and filtration by the mussels and the provision of a structurally complex habitat.

The influence of Cryptocotyle lingua (Digenea:Platyhelminthes) infections on the survival and fecundity of Littorina littorea (Gastropoda:Prosobranchia); an ecological approach

Abstract This study considers the impact of digenean parasites, especially Cryptocotyle lingua (Creplin) on the survival, reproduction, growth rate and foot colour of Littorina littorea (Forbes and Hanley). An 18 month field experiment demonstrated decreased survivorship of infected snails. A laboratory experiment showed a drastic reduction, but not total cessation, of gamete production in infected females. Infection was found to retard growth and correlate with reduced shell height in some animals. A strong relationship was found between foot colour and infection. The relevance of infection to the population dynamics of L. littorea on the Ythan, and to the Ythan food web as a whole, is considered.

Compartments and predation in an estuarine food web

The proposition that strong functional predator-prey links are associated with compartments in food webs (Paine 1980) is examined for a large, well-documented web, the Ythan estuary. A simple method for the detection and description of infrastructure within binary food webs is described and this is applied to 12 webs previously analysed by Pimm & Lawton (1980) and to the Ythan web. There was evidence for significant compartmentation in several real webs, all of which are reasonably well documented, aquatic and benthic. However, there was no evidence of compartments in the Ythan web

The accumulation of copper, zinc and cadmium by the amphipod Corophium volutator (Pallas)

In this study, sediment bioassays and behavioural tests were conducted on the marine amphipod Corophium volutator exposed to copper, zinc and cadmium following the standard US EPA/COE amphipod sediment bioassay protocol. The metals affected burrowing behaviour of Corophium in a dose-dependant manner. Corophium survival was higher for all metals when sediment was present than when sediment was absent, although metal body burdens were the same in both cases. Bioconcentration factors (BCF) for Cu, Zn and Cd were inversely related to seawater metal concentrations. When allowed to choose between contaminated and clean sediment presented at small spatial scales, Corophium avoided contaminated sediment, the proportion showing this behaviour increasing with the degree of contamination. When cadmium and zinc were added together, cadmium was less toxic and tissue concentrations were reduced. These results are discussed in relation to possible interaction mechanisms.

The role of the predatory crab, Liocarcinus depurator, in a marine food web

SUMMARY (2) Cages covering 1 m2 maintained crab densities from zero to eight crabs m-2 (0-32 times natural densities) for a period of 24 days. The total number of prey individuals, the number of species in samples and abundance of selected species were compared between treatments using ANOVA. Overall differences in assemblages were explored using multidimensional scaling. Effects on population size structure for four common species were also examined. (3) Contrary to expectation, there was little evidence that predation by Liocarcinus had any significant effect on the abundance of benthic species. The number of species in samples and the total number of individuals in samples were not significantly different between treatments and there were no effects on individual species which could be interpreted in terms of predation. The multivariate analysis, however, suggested some effects of caging, possibly due to the exclusion of other predators in addition to crabs in the case of infauna.

Induction of cytochrome p-450 monooxygenase activities in plaice by ‘model’ inducers and drilling muds

Abstract The hepatic cytochrome P-450-dependent monooxygenase system of the marine fish plaice has been characterised by i.p. injection with chemical inducing agents, followed by measurement of a variety of monooxygenase activities. The results suggest that more than one isozyme is present in these fish. The response to oil-based drilling fluids, a major contaminant of the North Sea, has also been examined and indicates that more than one isozyme is responsive to these products.

The effect of larval trematodes on the growth and burrowing behaviour of Hydrobia ulvae (gastropoda:prosobranchiata) in the Ythan estuary, north-east Scotland

Hydrobia ulvae were collected from five areas on the Ythan estuary, and the prevalences of digenean parasites in the samples compared. Differences in mean shell height were best explained by differences in parasite prevalence. All snails larger than 6.1 mm were infected, with a strong correlation between size and probability of infection. Comparisons of depth distributions of different size classes of snail in the substratum showed that larger snails were disproportionately represented in the top 5 mm. Snails exposed on the surface of the mud at low tide were found to have a higher chance of infection with metacercarial species compared with those that were buried. Snails infected with metacercarial species were less likely to burrow than those infected with other species, or with uninfected snails, in laboratory experiments. Large snails crawled more slowly and did not react as rapidly to simulated rainfall as small snails. These observations are interpreted as evidence for parasite-induced changes in snail behaviour.

An assessment of the potential of major meiofauna groups for monitoring organic pollution

Abstract The numbers of six meiofauna groups (nematodes, copepods, turbellarians, archiannelids, oligochaetes and gastrotrichs) were estimated from 17 sandy beaches differing in their organic (sewage) pollution loadings. Nematodes were most abundant on polluted and fine sand beaches whilst copepods were more common on coarse sand and rare on polluted beaches. The ratio of nematodes to copepods may thus provide a useful index of beach quality. Archiannelids and oligochaetes seem restricted to particular habitat types and, with the turbellarians, have little potential for biomonitoring. Gastrotrichs occurred in large numbers on one polluted beach.

Patterns of distribution

Most biology or environmental sciences students will at some time or other visit the shore as part of their education, many taking a formal course in intertidal ecology. One of the reasons why the intertidal area is such a valuable teaching aid is that the distribution patterns of the major groups of organisms change rapidly on the sharp gradients between sea and land and these are clearly modified by wave action. Moreover, these patterns can be easily seen and described — especially the horizontal bands or zones of conspicuous organisms like barnacles and seaweeds on rocky shores.

The importance of flatfish predation and disturbance on marine benthos: an experiment with dab Limanda limanda (L.)

Abstract The impact of predation and disturbance by dab Limanda limanda (L.) on the abundance of benthic fauna has been examined using cages to manipulate fish densities. Single dabs were enclosed in cages covering 1 m 2 for 24 days and prey numbers were compared with those from empty cages and uncaged areas. Dabs held in cages failed to feed and lost weight despite the presence of known prey in samples. Supplementary tests indicate that the absence of feeding was not the result of a stress related loss of appetite. Small but consistent reductions in the numbers of some prey species in cages containing fish suggest a disturbance effect. However, these effects were not marked. We suggest that neither predation nor disturbance by dabs is likely to be important for the prey community and that, although present, most prey are unavailable for most of the time and dabs have to forage widely to obtain sufficient food.